1. Field of the Invention
The invention relates generally to the flight system for a constant volume, variable buoyancy air vehicle able to achieve vertical takeoff and landing utilizing lighter-than-air static lift principals and achieving forward flight by utilizing heavier-than-air dynamic lift principals. More particularly, this invention relates to a flight system combining an aerodynamically efficient hull filled with lifting gas and incorporating a system for controlling the pressure of a lifting gas in a constant volume envelope and the ability to adjust buoyancy by actively compressing or decompressing the lifting gas, with the resulting pressure differential being borne essentially by an internal pressure tank.
2. Background of the Invention
There are two types of air vehicles currently operating that use lighter-than-air gases for lift: conventional airships that use primarily static lift and hybrid airships that combine static lift and aerodynamic lift. Both vehicle types are based on a variable volume of lighter-than-air gases design that depends upon using ballonets (internal air cells inside of the envelope).
Referring to FIG. 3, conventional airships use lighter-than-air gases such as helium to create positive lift. Such airships are always lighter-than-air and require ground crews and equipment to assist during takeoff and landing. The ground crews must also supply and remove ballast, such as sand or water to compensate for payload/cargo weight. Such airships are altitude limited because of pressure height limitations established by the size of the ballonets contained within the airship.
Referring to FIG. 4, hybrid airships are always statically heavy. They are either shaped as lifting bodies or equipped with lifting devices. Such vehicles typically possess wings to generate aerodynamic lift. Aerodynamic lift allows the hybrid airship to take off when statically heavy. An airship that remains persistently statically heavy compensates for weight loss due to fuel burn and cargo offloading. Statically heavy airships can also eliminate the ground crews/equipment needed by conventional airships. However, hybrid airships require runways for takeoff and landing.
Both conventional airships and hybrid airships require the use of one or more ballonets. Ballonets are required because variables such as temperature, altitude, density, superheat and atmospheric pressure all affect the state of the lifting gas inside the hull of the airship during flight. These variables cause the lifting gas to either contract or expand. For example, as the airship climbs during flight the atmospheric pressure decreases and the lifting gas inside the envelope expands, thereby increasing the internal hull pressure. As the airship descends, the reverse occurs: atmospheric pressure increases and the lifting gas inside of the hull contracts. Ballonets equipped with blowers and air valves are used to adapt to the pressure changes caused by expanding and contracting lifting gas within the airship. Ballonets are bags inside the envelope into which air is either forced in or out. Referring to FIG. 6, the ballonet 6 is primarily used in flight to control hull pressure during ascent and descent. Ballonets are also used to counter variations in lifting gas volume that occur as a result of diurnal temperature changes and weather pattern movements. Once the ballonets are emptied, the airship is said to be at pressure height 8. Once at pressure height the airship cannot climb any higher without releasing lifting gas from the hull. Referring to FIG. 7, an aircraft 10 using a volume compensation system other than a ballonet may have a dramatically increased pressure height 8.
Conventional airships and hybrid airships are not presently used for cargo transportation for a number of reasons. Ballonets limit the vehicle's operational altitude. Ballonets also increase the total vehicle size which in turn leads to larger and less manageable vehicles. Conventional and hybrid airships require ballast such as sand or water, which makes cargo offloading more difficult. Supplying ballast requires large ground crews and ground handling infrastructures. Hybrid airships require oversized runways to accommodate the vehicle size and are not able to perform vertical takeoff or landing.
In order to overcome the limitations of conventional and hybrid airships, it would be desirable to control the lifting gas volume within an aircraft, at least during cruise conditions, by maintaining the lifting gas at constant volume. Such a system would reduce the need for ballonets or at least minimize their undesirable effect of limiting the pressure height of such an aircraft.
Today, pilots of conventional and hybrid airships have little control over the buoyancy of the aircraft. Typically, they can either dump ballast to increase static lift or release the lifting gas to decrease static lift. Various systems for buoyancy control have been discussed in the art, and in particular, systems for compressing and releasing helium from a pressure tank onboard an airship have been discussed. None of these designs have come to fruition however, i.e. they remain merely theoretical concepts that have not and likely never will become actual flying aircraft.
Moreover, those prior art helium compression systems that have been suggested advise the use of high pressure helium pumps to control the flow of helium within the airship. High pressure helium compression systems have substantial disadvantages and, in particular, are too heavy and too slow to respond to changing volume conditions within the airship. In addition, they require heavy active cooling systems to keep the helium gas at a useable temperature.
Therefore, there remains a need in the art for a system of compressing and decompressing a lifting gas in a buoyant aircraft for the purpose of maintaining buoyancy control that is relatively lightweight and can respond quickly to changes in the lifting gas volume.